Alginate fibers are well known and widely used in wound dressing materials. For example, a knitted alginate is currently being marketed as Ultraplast.TM. styptic gauze wound dressing by Wallace, Cameron & Co. Ltd., Glasgow, Scotland. Furthermore, a carded web of alginate fibers is being marketed as Steriseal Sorbsan.TM. surgical dressing by N.I. Medical, Redditch, Worcestershire, England, and a carded and needle-tacked web of alginate fibers is being marketed as Kaltostat.TM. hemostatic wound dressing by Cair Ltd., Aldershot, Hatt, England. Additionally, alginate tow is marketed by each of the latter two companies under the same tradenames for use as wound dressings and surgical packings.
It is stated in U.S. Pat. No. 4,704,113 (Schoots) that two important functions of surgical or wound dressings are the ability to absorb and hold liquid and the ability to wick and transfer exudate of a wound away from the wound site. Furthermore, clinical testing has established that the healing of a wound is enhanced by keeping the wound bed moist. Thus a wound dressing should absorb and transfer wound exudate away from the wound surface without desiccating the wound bed. Additionally, the wound dressing should release from the wound easily without causing damage to the newly formed tissue.
Although the fibrous alginate wound dressings mentioned above perform these functions well, there are many inherent disadvantages associated with their use. Except for the knitted Ultraplast.TM. wound dressing, each of the aforementioned commercial alginate products is difficult to handle. The Steriseal Sorbsan.TM. dressing has poor structural integrity and tends to shed fibers when dry. Because of this weakness, skill is required to apply the dressing to wounds, and handling problems are aggravated when ones fingers are not completely dry. The Kaltostate.TM. dressing has better structural integrity but has a relatively high basis weight of about 160 g/m.sup.2 and is not as supple as would be desired for most applications. Additionally, because alginate fibers are highly absorbent, dressings based on high basis weight webs of the fibers are more likely to desiccate a wound if applied to the wound in a dry condition. The manufacturer of the needle-tackled Kalostat.TM. dressing avoids this problem by recommending that the dressing be moistened before application to the wound.
Although the knitted Ultraplast.TM. wound dressing has good integrity when dry, it becomes weak and loses its integrity when saturated with saline or body fluids. This loss of integrity causes the Ultraplast.TM. wound dressing to disintegrate while being lifted from a wound (as do others of the commercial alginate dressings cited above), necessitating that it be picked out in tiny pieces or removed from the wound by irrigation. Because removal by irrigation is a complicated and messy process that requires a substantial degree of skill, users prefer wound dressings that can be lifted from a wound in a single piece.
Nonfibrous alginate wound dressings are also known in the art. For example, U.S. Pat. No. 4,393,048 (Mason, Jr. et al.) discloses a wound dressing comprising a water-soluble hydrogel of alkali metal alginate and glycerin. These wound dressings are said to be prepared by applying a gel composed of water, alkali metal alginate and glycerin to a wound, and allowing the composition to air dry to form a water-soluble flexible film. It is stated to be an advantage of these dry film dressings that they are water-soluble and can be removed by water washing. However, as stated above, water washing is messy and is less desirable than removing the dressing from the wound in one piece. Furthermore, these wound dressings probably do not function well in highly exuding wounds where it would likely take an unreasonably long period of time for the material to air dry; if such air drying can be accomplished at all.
Additionally, Swedish Patent Application Publication No. 424,956, published Aug. 23, 1982, discloses a water-insoluble alginate hydrogel wound dressing. This dressing is said to be prepared by mixing water-soluble alginate, a soluble metal salt having metal ions that react with the water-soluble alginate to form a crosslinked water-insoluble alginate, and water to form a reactive cream-like paste that is spread over the wound surface. After application to the wound surface the constant progression of the crosslinking reaction transforms the cream-like paste into an elastic rubber-like composition. It is stated that because of the dressing's composition it will have a fluid absorbing effect after it is converted into the elastic condition, and will evaporate moisture from its outer surface. While these properties are generally desirable in a wound dressing, the absorption of fluid by the disclosed hydrogel dressing must either be limited by the evaporation of fluid from the gel surface or must be accompanied by an undesirable swelling of the gel. If the absorbency of these dressings is controlled by the evaporation of fluid from the dressing surface, these dressings will be of limited utility for heavily exuding wounds as their absorbency will probably be too low to prevent a build up of wound exudate at the wound surface. If the dressing swells upon the absorption of fluids, this lack of dimensional stability may severely undercut the utility of these dressings for packing deep, heavily exuding wounds. When a deep, heavily exuding wound is packed with this gel the swelling which may accompany the absorption of fluid may cause the dislodging of the packing, unless the packing is restrained within the wound by an outer wrap of some form. However, if the gel is so restrained that it cannot swell, the fluid absorbing properties may be undesirably reduced.